An agricultural work vehicle which is called ‘tractor’ is structurally similar to general cars, but it has a powerful engine so that it has good traction force and is strong. As a result, the tractor is generally used for cultivation in agricultural work, and so as to perform the cultivation, further, the tractor has various kinds of agricultural work machines detachable attached to the rear side of the body thereof.
So as to improve the efficiencies of the work, the agricultural work vehicle has to have a large gear-shifting range so that a driving speed and a rotational speed of a power take off (which is referred to as ‘PTO’) shaft can be adjusted to optimal speeds according to qualities of soil under the work, and accordingly, the agricultural work vehicle adopts a transmission complicated in structure and having a large gear-shifting range.
FIG. 1 is a sectional view showing a conventional transmission assembly for an agricultural work vehicle.
Referring to FIG. 1, a conventional transmission assembly for an agricultural work vehicle largely includes a transmissions 1 and a rear differential 6. The transmission 1 includes a shuttle gear-shifting unit 2 for forward/backward gear-shifting, a main gear-shifting unit 3 and a sub gear-shifting unit 4 fox providing a large gear-shifting step range, and a front wheel driving unit 5 for performing bi-speed turn and front wheel driving, and the rear differential 6 is adapted to appropriately distribute the power gear-shifted by the transmission 1 to left and right rear wheels.
The shuttle gear-shifting unit 2 of the transmission 1 is a hydraulic multi-plate clutch for performing selective power connection by the pressure oil whose flowing is permitted by the lever manipulation of a driver, and the main gear-shifting unit 3 has a synchronized multi-stepped (four seep) gear. The sub gear-shifting unit 4 has pairs of gears having different gear ratios moving to left and right sides by means of lever manipulation in such a manner as to be selectively engaged with each other.
The front wheel driving unit 5 is a hydraulic multi-plate clutch in the same manner as the shuttle gear-shifting unit 2. The various components constituting the transmission 1 and the rear differential 6 are located protectedly in a closed space formed by a transmission ease 8, and oil as a lubricating agent is filled in the transmission case 8 so as to achieve gentle power transmission between gears, gentle shaft rotation, and friction and abrasion reduction between components.
A reference numeral 7 nor explained yet in the figure indicates a PTO gear-shifting unit for taking off the engine power from the vehicle body so that the power generated from the engine is utilized as the power for driving the work vehicle.
However, the conventional transmission assembly for the agricultural work vehicle is complicated in structure, thereby causing high manufacturing costs and low assemblability and productivity, and is bulky in whole volume, so that if it is applied to a small-sized agricultural work vehicle having small wheel sizes, it is hard to ensure ground clearance or to provide a low-floor vehicle with a driver's seat having a low height.